On the edge of the Carneddau range of mountains in Snowdonia lays the deepest lake in North Wales, Llyn Cowlyd. The lake has been dammed so it is unnaturally deep, but it has given soundings of 229 feet, and has a mean depth of 109 feet. The lake is almost 2 miles long, and a third of a mile wide, with the adjacent hills dropping steeply to the lakes edges.
The lake has numerous legends attached to it:
1) It is allegedly the home of a Ceffyl Dŵr (Water Horse). These creatures are said to be able to shape shift and fly. Though they appear solid, they can quickly evaporate into mist.
2) It is reputed to house a ‘Water Bull’, which appears from the depths with “fiery horns and flames issuing out of its nostrils”.
3) It is said to be a place where witches were thrown. Those that survived were evidently demonic, and the ones that drowned were blameless.
4) There are tales of lone walkers that have been dragged to their death.
5) The lake is said to be the home of the Tylwyth Teg (Welsh Fairies).
In The Mabinogion, the story of Culhwch and Olwen mentions a number of mythical beasts, one of which is the Owl of Cwm Cowlyd, which narrates the history of the valley, indicating that it was once mainly wood land, if these stories are to be believed.